(This is the way the world ends - not with a bang, but with a sticker-shock whimper.)

Fortunately, that's of zero concern to Robert Neville (Will Smith), who as the last man on Earth enjoys certain perks, free fill-ups among them. (Self-service only.)

Neville guns his muscle car through whisper-quiet Manhattan as if he's got a show to catch. But Times Square is now a concrete-walled pasture, prowled by real-life lion kings.

The vistas in "I Am Legend" of a people-free New York are a thing of utter wonder, done with little digitization and a creepy feel for a city gone to seed (and weed).

Long before Neville's ride needs a top-off, though, the movie is running on fumes. Director Francis Lawrence and writers Mark Protosevich and Akiva Goldsman have taken Richard Matheson's 1954 novel, with its subversive twist on subjects of social justice, and made what's mostly a straight-up monster mash.

It doesn't cheat on the chills: Some moments might make even the most scare-resistant leap outta their seats. But no one's brain is going to break a sweat.

Except maybe Smith's. He plays Neville as a tortured warrior, an Army scientist still insisting "I can fix this" to no one in particular, three years after his efforts as chief virus-fighter failed to stop the killer epidemic.

Billions died, and the relatively few who didn't became the new face of New York's nightlife, cowering in the dark and waiting for the odd morsel (deer, dog, the exceedingly rare human) to blunder by. In the book they were garden-variety vampires; here they're like muscled zombies on a Red Bull bender.

Barricaded in a brownstone hard by Washington Square Park, Neville spends nights testing serums on seriously ghastly captives, and days chatting up mannequins at the video shop.

Smith carries the burden of sadness and apprehension beautifully, and when a mom and son survivor (Alice Braga, Charlie Tihan) straggle in, he conveys Neville's mute mix of confusion, anger, joy and disbelief with taut economy.

Then things turn squishy. The newcomer Anna, following guidance from on high, is headed to a hypothetical survivors' compound in Vermont, where refugees presumably huddle behind a protective moat of maple syrup.

Neville scoffs, then senses a mystical message, too. The climax, surprising or not, proceeds to wrap up so fast you might wonder if the zombies scarfed a few pages of script.